//  This file is part of YamlDotNet - A .NET library for YAML.
//  Copyright (c) Antoine Aubry and contributors

//  Permission is hereby granted, free of charge, to any person obtaining a copy of
//  this software and associated documentation files (the "Software"), to deal in
//  the Software without restriction, including without limitation the rights to
//  use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
//  of the Software, and to permit persons to whom the Software is furnished to do
//  so, subject to the following conditions:

//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.

//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.

using System;
using System.Collections.Generic;

namespace YamlDotNet.Core
{
    /// <summary>
    /// Implements an indexer through an IEnumerator&lt;T&gt;.
    /// </summary>
    public class FakeList<T>
    {
        private readonly IEnumerator<T> collection;
        private int currentIndex = -1;

        /// <summary>
        /// Initializes a new instance of FakeList&lt;T&gt;.
        /// </summary>
        /// <param name="collection">The enumerator to use to implement the indexer.</param>
        public FakeList(IEnumerator<T> collection)
        {
            this.collection = collection;
        }

        /// <summary>
        /// Initializes a new instance of FakeList&lt;T&gt;.
        /// </summary>
        /// <param name="collection">The collection to use to implement the indexer.</param>
        public FakeList(IEnumerable<T> collection)
            : this(collection.GetEnumerator())
        {
        }

        /// <summary>
        /// Gets the element at the specified index. 
        /// </summary>
        /// <remarks>
        /// If index is greater or equal than the last used index, this operation is O(index - lastIndex),
        /// else this operation is O(index).
        /// </remarks>
        public T this[int index]
        {
            get
            {
                if (index < currentIndex)
                {
                    collection.Reset();
                    currentIndex = -1;
                }

                while (currentIndex < index)
                {
                    if (!collection.MoveNext())
                    {
                        throw new ArgumentOutOfRangeException("index");
                    }
                    ++currentIndex;
                }

                return collection.Current;
            }
        }
    }
}